The purpose of this research study is to test the safety and effectiveness of ABT-378/ritonavir in combination with d4T and 3TC in HIV-infected men and women who are at least 18 years old. There will be approximately 32 subjects in Group I and approximately 70 subjects in Group II. Group II will be enrolled based on a review of existing safety data from 16 subjects in Group I. This review indicated that no serious adverse events have occurred.